Amal carbs and spark plugs issues and concerns

[franko]

Although not on my Norton, but when I set the carbs on my 85 BMW R80RT, I used non ethanol gas available here. She ran fine. When I rode down to visit my brother in Texas and was not always to buy non ethanol gas, a slight popping on deceleration would occur. In my mind, it was the slight difference in gas that caused the problem, with the ethanol making the bike run leaner. I also have a story about the gas I bought in Hudson on that trip.

 

[Tornado]

Ok, so I got the new NOS float in and the carbs back together without adjusting the float level (still a mystery to me) and went from the PO's Champion RN9YC plugs at .030" gaps to NGK BPR7ES plugs at .025" in an effort to make it run less rich and less hot. When that was popping too much on a test run on strong downshifting I went back to new Champions that the PO was using and gapped them at .025. Ran better but still had some popping on mid to higher RPM downshifts 4th to 3rd and 3rd to second. If I can get this worked out I think I'm good to go for a while. Should I go back to the wider gap or an even tighter gap or try the Champion RN7YC with a gap in what range? I have a recent Boyer electronic ignition and a choke but so far unused. The previous owner also didn't use the choke.

Im pretty sure I'm correct on this, changing plug gap and heat range does not influence engine temperatures nor popping in exhaust. Heat range of a plug is a measure of how well the plug shed its heat, with the idea to get it correct range for the plug to reach self-cleaning temps over the engine operating temp range. Too hot a plug will lead to premature electrode degradation, too cool a plug will lead to excessive carbon fouling. Gapping is important to be within the capabilitues of the ignition setup. Just go with the book specs for the bike.
Lots of popping on my bike was a sign of over lean condition, solved by properly cleared carb jets, proper sized un-worn needle and needle jet, no air leaks inlet mani fold joints, well fitting, non perished cross tube on inlets, and properly balanced carb slides.

When you next get popping, try applying the choke to see if popping changes or stops, which would indicate engine too lean and you need to find why. Dont forget, choke lever on these carbs must be fully tight on the cable for choke OFF. Many have made that mistake.

 

[arcpoint]

Im pretty sure I'm correct on this, changing plug gap and heat range does not influence engine temperatures nor popping in exhaust. Heat range of a plug is a measure of how well the plug shed its heat, with the idea to get it correct range for the plug to reach self-cleaning temps over the engine operating temp range. Too hot a plug will lead to premature electrode degradation, too cool a plug will lead to excessive carbon fouling. Gapping is important to be within the capabilitues of the ignition setup. Just go with the book specs for the bike.
Lots of popping on my bike was a sign of over lean condition, solved by properly cleared carb jets, proper sized un-worn needle and needle jet, no air leaks inlet mani fold joints, well fitting, non perished cross tube on inlets, and properly balanced carb slides.

When you next get popping, try applying the choke to see if popping changes or stops, which would indicate engine too lean and you need to find why. Dont forget, choke lever on these carbs must be fully tight on the cable for choke OFF. Many have made that mistake.

Will do, thanks. What are the general causes/solutions when running too lean?

 

[arcpoint]

What is “strong downshifting?”

Under what throttle and rpm conditions does popping occur?

Is it the exhaust that is popping, or the intake?

When I ride gently in the lower RPMs no popping, maybe a little almost unnoticable unsmoothness, only when I am rapidly throttling down from higher RPMs and downshifting does the popping occur. And yes, Id say exhaust popping but then I can't say for sure as I didn't know there was such a thing as intake popping. It's not firecracker loud like a major backfire but some mid decibel pops.

 

[acotrel]

Will do, thanks. What are the general causes/solutions when running too lean?

Lift the needles one notch.

 

[worntorn]

Ok I'm quite happy to be shot down in flames here
But has anyone noticed any appreciable difference when adjusting float height on Amal concentrics?
I've played with adjusting float height in the past but have never noticed a difference
Maybe it's just me
But as long as the float isn't too high and flooding
Or way too low I can't honestly say I've noticed a difference?

Same, but I have never had the nerve to say so on a public motorcycle forum.
It's like admitting you can't tell the difference in handling with tires at 28 psi vs 32. And I'm not admitting to that either!

Glen

 

[arcpoint]

Lift the needles one notch.

Thanks, will do.

 

[Tornado]

Running overly lean can be due to anything that introduces more air into the mix. As i srsted what cured it on my bike was a series of checks and changes, not sure what ultimately cured all signs of over lean. But gotta confirm no air leaks at carb ro inlet, inlet to head, the cross tube between the spigots on inlet manifolds, ensure you have recommended jets in the carb (needle and needle jet, main jet and if premier carb, removable pilot jet is correct). Are throttle slides smooth in bores or loose? Are carb jets clear, spray cleaner flows fully and sprays up out the two very tiny holes in carb throat? Blockages anywhere will make for poor running/idling and forcing otger settings to be way out to set idle, thus incorrect mixture while running.

A good idea for troubleshooting, outlined in the amal concentric carb guide pamphlet and most brit bike manuals, figure out what jets are operating in the problem throttle positions. Make somectape marks on your grip and note where it is when you get the popping. This will inform where throttle slide is and thus which jets are operating there.

 

[arcpoint]

Running overly lean can be due to anything that introduces more air into the mix. As i srsted what cured it on my bike was a series of checks and changes, not sure what ultimately cured all signs of over lean. But gotta confirm no air leaks at carb ro inlet, inlet to head, the cross tube between the spigots on inlet manifolds, ensure you have recommended jets in the carb (needle and needle jet, main jet and if premier carb, removable pilot jet is correct). Are throttle slides smooth in bores or loose? Are carb jets clear, spray cleaner flows fully and sprays up out the two very tiny holes in carb throat? Blockages anywhere will make for poor running/idling and forcing otger settings to be way out to set idle, thus incorrect mixture while running.

A good idea for troubleshooting, outlined in the amal concentric carb guide pamphlet and most brit bike manuals, figure out what jets are operating in the problem throttle positions. Make somectape marks on your grip and note where it is when you get the popping. This will inform where throttle slide is and thus which jets are operating there.

Thanks. I'm going to try all the things I can without removing the carbs first, then move onto the removal and teardown process. Thos seems a little extreme as they were recently rebuilt with little mile on them. Which brings me back to considering other options. I get that these are relatively simple but seem so fragile. The Amal lovers on thos site definitely present a good case for keeping them but I can't help but wonder if being a purist has its price. And maybe just maybe there are a few of these guys just want to sit back in their man caves throwing one back with a laugh knowing that they are sending neophytes on a maddening year long quest to tame these buggers. I don't mind tinkering, in fact I enjoy it, but I greatly prefer more riding than tinkering. And I am not hyper knowledgeable in the areas of combustion engines nor have the youth or strength to rips these bikes apart and throw them back together again. That's why I bought one that had been 90% restored. We'll see how it all turns out. Now I think I'll go for a ride, popping and all. And hopefully make it back home. On my bike.

Lastly, why all major adjustments aren't incorporated from the outside of the carbs for the general life of them is my main point of contention. Then I ponder Keihins (flat or the other option which I forget the name) or twin Mikunis (like I had on an old Yamaha XS 650 bored to 750). Or lastly, as soamy resort to, a single Mikuni. And if it all proves too too much for me then I will have to throw in The towel and end up a statistic in the graveyard of failed Norton wannabe enthusiasts.

At least I'm trying.

 

[baz]

Same, but I have never had the nerve to say so on a public motorcycle forum.
It's like admitting you can't tell the difference in handling with tires at 28 psi vs 32. And I'm not admitting to that either!

Glen

I try to only talk about things I have actually done myself and the conclusions I come to

 

[ashman]

A well set up Amals the Norton's run so well with them, its when they sit around and not being ridden is when you will have troubles with them, they are the easiest carbs to work on, they are so simple, easy to tune, but things do wear like jets and needles from vibrations, but E10 fuel seems to be a big problem lucky we have a choice here in Aus and not forced to use E10 fuels.

 

[arcpoint]

A well set up Amals the Norton's run so well with them, its when they sit around and not being ridden is when you will have troubles with them, they are the easiest carbs to work on, they are so simple, easy to tune, but things do wear like jets and needles from vibrations, but E10 fuel seems to be a big problem lucky we have a choice here in Aus and not forced to use E10 fuels.

This is a major factor I'm having to consider as I'm in California where the gas is all ethanol. I've even tried the local airports and they look at me like I'm trying to break the law or something. Doesn't hurt to ask is all I'm saying.

 

[Tornado]

This is a major factor I'm having to consider as I'm in California where the gas is all ethanol. I've even tried the local airports and they look at me like I'm trying to break the law or something. Doesn't hurt to ask is all I'm saying.

The bikes run just fine on 10% ethanol. Pretty much all of North America and UK now run at least E10 for road engines. It's the concern of longer storage with ethanol sat in the float bowl/pilot circuits and potentially the tank that are the most worrying. Leaves a nasty precipitate when it all evaporates away with storage.

 

[marshg246]

Might just be terminology, but IMHO, popping is poor/lean mixture in the cylinder(s). Loud bangs are unburnt gas exploding in the hot exhaust pipes (too rich). True backfires are pre-ignition (explosions in the cylinders) and are not nearly as loud as explosions in the exhaust.

 

[arcpoint]

The bikes run just fine on 10% ethanol. Pretty much all of North America and UK now run at least E10 for road engines. It's the concern of longer storage with ethanol sat in the float bowl/pilot circuits and potentially the tank that are the most worrying. Leaves a nasty precipitate when it all evaporates away with storage.

Yeah, that's what I've heard, that the best thing for them is to keep them gassed up and frequently ridden.

 

[arcpoint]

Might just be terminology, but IMHO, popping is poor/lean mixture in the cylinder(s). Loud bangs are unburnt gas exploding in the hot exhaust pipes (too rich). True backfires are pre-ignition (explosions in the cylinders) and are not nearly as loud as explosions in the exhaust.

I'm not sure what I'm hearing then. Will listen more closely. Because it isn't ovey loud. Just slightly annoying.

 

[Triton Thrasher]

When I ride gently in the lower RPMs no popping, maybe a little almost unnoticable unsmoothness, only when I am rapidly throttling down from higher RPMs and downshifting does the popping occur. And yes, Id say exhaust popping but then I can't say for sure as I didn't know there was such a thing as intake popping. It's not firecracker loud like a major backfire but some mid decibel pops.

I know of two possible causes of banging in the exhaust on over-run (throttle shut and engine slowing the bike down).

Loud bangs are caused by an air leak into the exhaust pipe, where it is attached to the cylinder head.
Not-so-loud bangs are caused by a weak idling mixture. That can be maladjustment of the mixture screws or an air leak into the inlet, between carburettor and cylinder head. You can test for such air leaks by spraying WD40 on the joints while the engine is idling slowly.

 

[arcpoint]

I know of two possible causes of banging in the exhaust on over-run (throttle shut and engine slowing the bike down).

Loud bangs are caused by an air leak into the exhaust pipe, where it is attached to the cylinder head.
Not-so-loud bangs are caused by a weak idling mixture. That can be maladjustment of the mixture screws or an air leak into the inlet, between carburettor and cylinder head. You can test for such air leaks by spraying WD40 on the joints while the engine is idling slowly.

Thanks. I will check these out and let you know what I find out.

 

[Grandad]

From my old car experiences a hole in a leaky silencer or its joint will produce popping on the overun.
( as well as fuel or timing issues)
Not wanting to open the debate on not using a silencer clamp on a commando but it may be worth applying some jointing where the silencer fits onto the downpipe irrespective of whether a clamp is used or not.

 

[acotrel]

A leak at the exhaust port is the usual cause for a backfire. Float levels do not matter much as long as they are the same in both carbs. Whatever fuel you use and whatever engine or exhaust system mods you have made the tuning sequence is the same. Fit the biggest recommended main jets. Start the bike, warm it up and set the idle so it is perfect when the engine is warm. That leaves the needles and needle jets to be adjusted. They operate when the throttle is open between one-third and two thirds. When you lower the needles, the mixture becomes leaner. If you lower them slightly too much, the engine will miss when you ride the bike. When you get that miss - raise the needles one notch. Main jets are not critical unless they are too lean. Jets meter fuel according to vacuum - they do not increase flow. Lean-ness gives more power but beyond a certain pont, can destroy engines.
Alcohol in fuel can cause zinc oxide to form in fuel bowls. So always drain the carbs if the bike is to remain stationary for more than a few days. I like Amal carbs better than Japanese. I think the Japanese use more zinc in their aluminium carbs. Alcohol attracts water.
The taper on the needles compensates for loss of vacuum when the throttle is being opened. If you are seeking better performance, try different taper needles. leaner needles affect the rate at which the throttle can be opened, but can help the bike to accelerate faster.